Humidifiers of various types are known. Steam generating humidifiers are advantageous. The boiling of supply water to produce steam tends to kill bacteria if present in the water reservoir. Minerals in the supply water tend to remain in the heated water reservoir. Thus a clean sterile vapor is distributed to the environment.
It is known to generate steam by immersing electrodes in a supply of water in the water reservoir so that the electric current flows through the water between the electrodes and heats same to generate steam. The current amperage, and thus the amount of steam generated, depends on the electrical conductivity of the water and on the depth to which the electrodes are immersed in the water. It is customary in such apparatus to use ordinary tap water having some degree of mineral content and to periodically drain some of the water in the evaporating tank to prevent an excessive build-up of mineral concentration, so as to keep the electrical conductivity of the water in a desired range. It is typical to monitor the amperage of heating current flow through the electrodes and to open and close a water fill valve controlling water inflow to the steam generator tank in response to heating current going above or below a desired range. A humidity sensing circuit may vary the range, for example to increase electrode current amperage and thereby steam generating rate, in response to a decrease in atmospheric humidity, thereby to increase atmospheric humidity to a desired level, wherein a manual adjustor selects the desired humidity level. An example of a prior art humidifier incorporating these features is shown in U.S. Pat. No. 4,146,775 assigned to the assignee of the present invention.
While the apparatus described above has provided generally satisfactory performance the present invention has resulted from a continuing effort to improve thereon.
It is customary to size the steam generator to at least meet the maximum expected steam output demand that may be encountered in the environment in which it is to work. However, when the demand for steam output is low compared to the maximum capacity of the unit, problems may result in some conventional steam generating humidifiers. In starting out from a cold condition, such a steam generator may tend to overfill and hence, as the water therein comes to a boil between the electrodes, the steam output may greatly exceed the level of steam production required, thereby causing a rapid rise in the humidity of the environment being humidified. If the steam output is very substantially greater than the desired steam output, the humidity level in the environment may rise to an unacceptably high level before the humidifier responds so as to terminate or reduce steam production. The steam output may remain off or at a very low level until the eventual fall in humidity in the environment again calls for opening of the fill valve and an increase in steam output, thus repeating the cycle. This on/off steam output is called "hunting" because the unit hunts for but never finds a steady operation condition. The net result tends to be an ongoing, unintended rise and fall in humidity in the environment.
Even during ongoing operation of the humidifier with the electrodes maintained partially immersed such that water therebetween is being vaporized, admission of cool fresh water to the boiler tank will raise the water level between the electrodes and thus increase electrode current but this may not immediately result in an increase in vapor output, until the freshly admitted fill water reaches the ambient temperature of the existing water in the boiler. Thus there may be some tendency to overshoot in vapor output after that temperature equalization takes place, particularly if the then maximum of electrode current and vapor output is substantially greater than that required to maintain the environmental humidity at the desired level. The typical conventional electrode-type humidifier will thus hunt in steam output repetitively above and below the level required to maintain the desired humidity level, particularly when the steam output required for a desired level of humidity is well below the maximum output capability of the humidifier apparatus.
Accordingly, the objects and purposes of the invention include the provision of:
a humidifier apparatus capable of automatically adjusting steam output capacity in response to a continuation, for more than a predetermined time, of a preselected humidity demand characteristic; PA1 an apparatus as aforesaid in which the humidity demand characteristic required for an increase in steam output may be an on/off humidistat remaining on, or a proportional humidistat signal remaining above some established level, for more than a predetermined time and such characteristic can further include an on/off humidistat remaining off, or a proportional humidistat signal remaining below some established level, for more than a predetermined time; PA1 an apparatus as aforesaid in which the output capacity of the humidifier will remain unchanged if, for example, an on/off humidistat cycles between on and off conditions during a predetermined length of time or if a proportional humidistat signal remains within a predetermined range for a predetermined length of time; PA1 an apparatus as aforesaid which substantially reduces the tendency of the apparatus to overshoot and undershoot the desired humidity level, i.e. to hunt, particularly where the level of humidity required in the environment requires a steam output considerably below the maximum capability of the humidifier apparatus; PA1 an apparatus as aforesaid capable of continuous modulated output; and PA1 an apparatus as aforesaid capable of providing various arrangements for flushing of the water tank to maintain mineral content in the water below a desired level.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following description and reviewing the accompanying drawings.